JPH02295222A - Discriminating device for proximity switch - Google Patents

Abstract

PURPOSE:To increase the accuracy of a proximity switch by storing the count value of a counter which is outputted when no metal exists around a detection coil, and deciding the presence of a metal when the detected count value is smaller than the stored count value by an amount larger than a prescribed level at the time of using the proximity switch. CONSTITUTION:A counter 11 counts previously the output pulse number 3a of a comparator 3 at the time of adjusting a proximity switch in a state where the metal to be detected within a magnetic flux produced by a detection coil L. The count value M of the pulse 3a is written into a memory 15 via a writing means 13. Then the value M written into the memory 15 is loaded to a count value deciding means 12A by a reading means 14 at the time of using the proximity switch. The means 12A compares the value A of the counter 11 that counted the number of pulses 3a with the threshold value (M-alpha) obtained by subtracting the prescribed value from the value M to decide the absence of a metal with A>=M-alpha and the presence of a metal with A<M-alpha respectively. Thus a proximity switch of high accuracy is obtained.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a discrimination device for a proximity switch, which discriminates whether or not a metal to be detected approaches the coil within the magnetic flux generated by the coil, which constitutes a damped resonant circuit by a coil and a capacitor, based on the speed at which the resonance decays. The present invention relates to a proximity switch discrimination device that can improve switch detection accuracy regardless of variations in component parts. Note that in the following figures, the same reference numerals indicate the same or corresponding parts.

[Conventional technology]

FIG. 2 is a circuit diagram showing a configuration example of this type of proximity switch (device), and FIG. 3 is a waveform diagram for explaining the operation of FIG. In Figure 2, L is a coil that determines whether a metal to be detected approaches itself within the generated magnetic flux, C is a capacitor connected in parallel to this coil to form a resonant circuit, and R
1 is a resistor for limiting the current flowing through the coil L, and S1 is a transistor driven via the pulse counting control circuit 2 to open and close the current of the coil L. Further, R2 and R3 are voltage dividing resistors for obtaining the reference voltage VF from the DC constant voltage power supply CC, and 3 is the voltage of the resonant circuit (in this example, the voltage at the connection point P between the resistor Rl and the transistor S1) and the reference voltage. This is a comparison circuit that compares VF. 2 is a pulse counting control circuit for opening/closing the transistor S1 and counting pulses, and 11 is a counter belonging to this circuit 2, which counts the output 3a of the comparison circuit 3. Now, when transistor S is turned on for a predetermined period of time to establish a predetermined current in coil L, which is approximately determined by DC voltage VCC and resistor R1, and transistor S1 is turned off, the potential at point P will be as shown in Figure 3 (1). , a damped oscillation waveform oscillates above and below the potential vCC. The comparison circuit output 3a obtained by comparing this P point potential and the reference voltage VF via the comparison circuit 3 is as shown in FIG. 3(2). In Fig. 3 (1) and (2), the waveforms on the left side indicate the case where there is no metal, that is, there is no detected metal approaching the coil L, and the waveforms on the right side indicate the case where there is metal, that is, the case where the detected metal does not approach the coil L. Indicates a case where there is close contact with metal. In this way, the attenuation of the resonant waveform becomes faster (stronger) as the metal to be detected approaches. This is because an overcurrent flows in the metal to be detected close to the coil due to a change in the magnetic flux generated by the coil L. When the pulse output as the comparison circuit output 3a is counted by the counter 11 in this manner, the counted value becomes smaller when the metal to be detected approaches than when it does not approach. Therefore, conventionally, the count output (number of pulses) A of the counter 11 is set to one threshold value (
N), if the number of pulses A was N or more, it was determined that there was no metal, and if it was less than N, it was determined that there was metal.

[Problem to be solved by the invention]

However, in conventional proximity switches, since the count value of the counter 11 is compared with a fixed value N, the attenuation waveform varies due to variations in the Q of the resonant circuits L and C, which causes an operation in which the presence or absence of metal is switched. The points varied due to the proximity switch, making it impossible to realize a high-precision proximity switch. Therefore, the present invention stores the count value of the counter when there is no metal to be detected within the magnetic flux generated by the detection coil or when the metal to be detected is placed at the desired position where detection is to be performed, when adjusting the proximity switch in advance. The count value of the counter detected and output when used as an actual proximity switch is set as a threshold value obtained by subtracting a predetermined value from the value stored in this memory, or as a value stored in the memory. An object of the present invention is to solve the above-mentioned problem by providing a discrimination device for a proximity switch that discriminates the presence or absence of metal by comparing it with a threshold value.

[Means to solve the problem]

In order to solve the above-mentioned problems, the device of the present invention “connects in parallel a coil (such as L) and a capacitor (such as C) arranged so that the metal to be detected can enter the magnetic flux it generates. to form a resonant circuit, and after applying a predetermined energization to this resonant circuit (using transistor Sl, resistor R1, etc.) via a DC power source (VCC, etc.), the DC power source is disconnected from this resonant circuit; After the disconnection of the coil or capacitor, the wave number of the attenuated resonant wave that occurs until the current or voltage of the coil or capacitor attenuates to a predetermined level is determined (via the comparator circuit 3, counter 11, etc.), and this wave number is calculated. ) In a proximity switch that determines (via pulse counting control circuit 2, etc.) whether or not the metal to be detected is in proximity to the coil by comparing with a predetermined counting threshold, The wave number of the damped resonant wave generated as described above is recorded (via the writing means 13, etc.) in a state where the metal is not within the magnetic flux generated by the coil L, or when the metal is placed at a desired position to be detected. ) and a means for storing and memorizing (such as the memory 15), and using this stored value (such as M), the counting threshold value (value M minus α obtained by subtracting a predetermined value α from the stored value M, or a stored value M, etc.). (as) setting means (writing means 14, count value determination means 12A, etc.).

[For use]

It is possible to determine that metal is present when the count value changes smaller than a predetermined value from a state in which there is no metal to be detected in the surrounding area, or to change the count value when used as a proximity switch to the state where no metal is actually detected. Highly accurate proximity detection of metal is performed by comparing the count value when placed at the desired position to determine the presence or absence of metal proximity.

【Example】

Next, an embodiment of the present invention will be described using FIG. This figure is a circuit diagram showing a configuration as an embodiment of the present invention, and corresponds to FIG. 2. In FIG. 1, the pulse counting control circuit is rotated in a new manner compared to FIG. Furthermore, a memory 15 is added outside the circuit 2A. Next, the operation of FIG. 1 will be explained using two embodiments. In the first embodiment, when adjusting this proximity switch in advance, the number of output pulses 38 of the comparator circuit 3 is counted by the counter 11 in a state where there is no metal to be detected in the magnetic flux generated by the detection coil L, and the counted value is Memo January 5 via writing means 13
It should be written and placed in the . In this case, when actually used as a proximity switch, the reading means 14 loads the value M written in the memo 1/5 into the count value determining means 12A, and this determining means 12
The value A of the counter 11 that counts the number of output pulses 38 of the comparator circuit 3 by A is compared with a threshold value M-α determined as the value obtained by subtracting a predetermined value α from the above M, and A≧M.
It is determined that there is no metal when -α, and there is metal when ARM-α. Further, as a second embodiment, when adjusting the proximity switch, the metal to be detected is placed at a desired position where the proximity of the metal to be detected is to be detected, and the number of output pulses 3a of the comparison circuit 3 at this time is counted by a counter. 11, and the counted value M is written into the memory 15 via the writing means 13. In this case, when actually used as a proximity switch, the reading means 14 loads the value M written in the memo January 5 into the count value determining means 12A as a threshold value, and the determining means 12A The value M is compared with the count value A of the counter 11 that counts the number of output pulses 3a of the comparator circuit 3, and it is determined that there is no metal when A≧M, and that there is metal when A<M.

【Effect of the invention】

According to the present invention, when adjusting the proximity switch, the counter count value output when there is actually no metal around the detection coil is stored in advance, and when used as a proximity switch, the counter count value output when there is no metal around the detection coil is stored in advance. It is determined that metal is present when the value is smaller than the memorized count value by more than a predetermined value, or when the metal to be detected is placed at the position where the proximity of metal is actually detected when adjusting the proximity switch. The output count value is memorized and when used as a proximity switch, the detected count value is compared with the threshold value as the memorized count value, so that the resonant circuits L and C are It is possible to effectively correct not only the variations but also the variations in Rl, R2, and R3, and a highly accurate proximity switch can be obtained.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing a configuration as an embodiment of the present invention, Fig. 2 is a corresponding conventional circuit diagram, and Fig. 3 is a circuit diagram of a corresponding conventional circuit.
FIG. 3 is a waveform diagram for explaining the operation of the figure.

Claims (1)

[Claims] 1) A coil arranged so that the metal to be detected can enter the magnetic flux it generates and a capacitor are connected in parallel to form a resonant circuit, and this resonant circuit is connected via a DC power source. The wave number of the attenuated resonant wave that occurs after the DC power source is disconnected from the resonant circuit after a predetermined energization is applied to the coil or capacitor until the current or voltage in the coil or capacitor attenuates to a predetermined level. In the proximity switch, which compares the number of signals with a predetermined counting threshold to determine whether or not the metal to be detected is in proximity to the coil, the wave number of the damped resonant wave generated as described above in a predetermined state is stored in advance. A proximity switch discriminating device comprising: means for storing; and means for setting the counting threshold using the stored value.